Switching generator voltage regulator having arc and spike suppression means



Dec. 16, 1969 H. MITTAG ET AL 3,4

SWITCHING GENERATOR VOLTAGE REGULATOR HAVING ARC AND SPIKE SUPPRESSION MEANS Filed Dec. 2, 1966 d 6 /5 7a 23 Ali/un- M v 4M United States Patent US. Cl. 322-23 7 Claims ABSTRACT OF THE DISCLOSURE A voltage regulating arrangement for maintaining the output voltage of an AC generator with a field winding constant. An electromagnetically operated contact is connected through a choke to the field winding. The movable contact switches between two fixed contacts one of which is connected to the grounded terminal of the generator. The other fixed contact causes the choke to be connected in parallel with a resistor having a positive temperature coefficient of resistance when the movable contact rests against the other contact. One terminal of the resistor is connected to the field winding and the choke. When the movable contact rests against the first fixed contact, the field winding is substantially short-circuited. A movable contact is operated by an electromagnetic coil connecte across the output terminals of the generator.

The present invention relates to a switching arrange ment in conjunction with a variable speed generator and, in particular, to an alternator having a shunt-field winding whose excitation current is controlled by a regulator of the vibrating type.

Switching arrangements of the preceding species have the disadvantage that the switching contacts become rapidly worn when applied to alternators. This arises from the fact that the operating conditions prevailing with AC-generators are considerably more severe than those prevailing with DC-generators. In AC-generators, the maximum current is limited through significant feedback action of the stator winding. This reflects upon the switching arrangement in the respect that it must deal with a substantially larger range of excitation current between idling condition and full load of the generator. For example, whereas the excitation current varies in the ratio of 1:2 between idling condition and full load in DC-generators, it varies in the ratio of 1:8 for corresponding AC-generators. This leads to the condition whereby the contacts of the switching arrangement either become severely eroded, pitted or seized to each other or are subjected within a short period of time to becoming pointed or spike-shaped to the extent that the actual contact arrangement becomes bridged.

Accordingly, it is an object of the present invention to provide a switching arrangement to operate in conjunction with an AC-generator, wherein the life of the switching contacts is significantly increased.

Another object of the present invention is to provide a switching arrangement of the character described, which is of simple design and construction.

A further object of the present invention is to provide a switching arrangement for operating in conjunction with AC-generators, which may be readily manufactured and installed.

A still further object of the present invention is to provide a switching arrangement, as set forth, which has a high degree of reliability and which may be maintained economically.

Patented Dec. 16, 1969 With the preceding objects in view, the present invention includes a choke connected at one end to a movable switching arm of the switching arrangement. The other end of the choke is connected to the shunt winding of the generator and to a thermistor. The switching arm is associated with two opposed stationary contacts. When using brushless AC-generators, for automobiles, the choke has preferably an inductance of L=4O to I whereby I is the average value of the excitation current. This average value of the current corresponds to that prevailing when the generator is delivering half its rated output and is driven at a speed corresponding to half the maximum value, and the proper voltage output is realized. The thermistor is designed so that it assumes a resistance value of approximately 2 /2 ohms, for full load of the generator, and approximately 8 ohms when the generator is in its idling state.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its additional objects and advantages thereof, will be best understood from the following description of specific emmodiments when read in connection with the accompanying drawing.

Referring to the drawing, a rotational generator 11 is driven by a motor within, for example, an automobile subject to considerable variation in speed. The generator is of an alternating current type, and is connected to the main load lines 12 and 13, by way of a three-phase rectifier (not shown). The supply or load lines 12 and 13 lead, by way of the diode 20, to a binary 14, as well as to a battery load, also not shown. The conducting path 13 is grounded.

The generator 11 has a shunt-field winding 15 with one end connected to the ground potential. The other end of the winding 15 is connected to a choke or induction coil 16 which is, in turn, connected to a movable contact arm 17. The latter is actuated by an electromagnetic coil 19 connected across the load lines 12 and 13, and is part of a switching arrangement 18. Aside from being electrically connected to the contact arm 17, the choke 16 is physically located within the vicinity thereof.

The contact arm 17 is biased towards the position, shown in the drawing, by a spring 17a. In this position the contact portion 22 of the switching arm 17 bears against the fixed contact 23. The latter is connected to a noise suppression choke 24 which is, in turn, connected to the main load line 12. The two contacts 22 and 23 are, substantially of a silver alloy having a copper content Within the range of 0 to 4%. As represented in the drawing, the fixed contact 23 is of greater dimensions than that of the contact 22, so that it does not become overheated as the result of a temperature increase that may develop in connection with the contact 22.

The lower section of the switching arm 17 has a contact portion 25 associated with a fixed contact 26. The contact portion 25 is made of a gold alloy having a nickel content within the range of 3 to 10%. The fixed contact 26 on the other hand is a silver alloy having a copper con tent within the range of 0 to 4%. The fixed contact 26 is connected to ground potential. The choke 16 is connected to the field winding 15 via a lead-through capacitor 27, as well as to a thermistor 28 having a positive temperature coefficient. The thermistor, on the other hand, is connected to the load line 12. A filtering capacitor 29 is connected across the main loadlines 12 and 13. The capacitor 29 also serves as a spark suppression component.

In operation, the switching arm 17 is initially in the position shown in the drawing, wherein the contact portion 22 bears against the contact 23. Under these conditions, an excitation current flows from the generator 11 to the field winding and thereby increases the output voltage of the generator 11. As a result, the magnetic coil or solenoid 19 actuates the switching arm 17 so that the contacts 22 and 23 become separated. The excitation current then takes the path through the thermistor 28 and thereby heats the latter so that its resistance value is increased. If, now, the voltage across the load lines 12 and 13 continues to increase, the switching arm 17 is further actuated by the solenoid 19 so that the contact portion is brought to bear against the fixed contact 26. This circuit configuration shorts the field winding 15 and prevents it from being further excited. As a result of such shorting of the field winding the output voltage of the generator 11 is reduced.

As a result of the continuous operation of the switching arms 17, in which it moves back and forth, the contacts associated with the switching arm are subjected to severe mechanical and electrical wear and pitting. Thus, the contacts 22 and 23 are subjected to a coarse deterioration whereby the contacts are worn down or become hooked together. The contacts 25 and 26, on the other hand, hecome pointed or spike-shaped, as a result of the preceding processes, and these spikes tend to bridge the contacts.

These undesirable wear effects are significantly reduced with the present invention. The latter provides, in this connection, for a choke 16 coupled to the field circuit and connected to the switching arm 17. For an AC-generator in an automobile, the choke should have an inductance Lofto60l where I is the average excitation current through the field winding 15. The choke 16 serves to suppress the high peaks of currents, arising from the inductance of the field, at the instant that the contacts touch.

The wear process of the switching contacts is further reduced through the application of the thermistor 28. With a high excitation current, this thermistor causes a reduction of the contact voltage when the switching arm 17 moves between the position shown in which the contacts 22 and 23 are engaged, and its centre position, when no contact is engaged. When the excitation current is lower and the movable contact member 17 moves between its centre position and the position, wherein contact members 25 and 26 touch, the thermistor 28 reduces the means switching current.

When used in a regulator for a typical alternator for use in an automobile, the thermistor 28 increases its resistance from approximately 2.5 ohms when the alternator is fully loaded to approximately 8 ohms when the alternator is running without load.

The life of the switching arrangement is further increased as a result of the special design of the contacts 22, 23, 25 and 26, as described supra. When taken together all three features of the invention function to increase the life of the switching arrangement, as used in the prior art, by a factor of 3. In accordance with the invention, moveover, it is possible to maintain continuous operation between idling condition and full-load, when utilizing an AC-generator.

While the invention has been illustrated and described as embodied in switching arrangements for automobile generators, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the invention.

Without further analysis the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the 4 standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A switching arrangement for AC generators having a shunt field winding comprising, in combination, a movable switching contact movable between a first and second switching position; electromagnetic means connected to the output of said generator and actuating said movable switching contact when energized by said generator; choke means connected between said shunt field winding and said movable switching contact for suppressing high peaks of currents arising from the inductance of said field; a stationary contact connected to the output of said generator and engaged by said movable switching contact when said electromagnetic means is substantially deenergized corresponding to substantially low voltage output of said generator; another stationary contact connected to said shunt field winding and engaged by said movable switching contact for short-circuiting said shunt field winding when the voltage output of said generator is above a predetermined level; and a contact portion secured to said movable switching contact and interposed between said stationary contact and said movable switching contact, said stationary contact being substantially larger than said contact portion for reducing the temperature attainable due to heat transfer from said contact portion to said stationary contact.

2. A switching arrangement as defined in claim 1, wherein said choke has an inductance between 40 and 60 nH/A I, whereby I is the average value of the current through said field winding.

3. A switching arrangement as defined in claim 1, wherein said stationary contact and said contact portion are of silver containing copper less than 4%.

4. A switching arrangement as defined in claim 1, wherein said other stationary contact is of silver having a copper content less than 4%.

5. In a vibratory voltage regulator for maintaining the output voltage of a generator having a field winding substantially constant, the combination comprising a movable contact member and two opposed stationary contact members, a choke connected to said movable contact member and located in the immediate vicinity thereof, resistor means having a positive temperature coefiicient of resistance and so connecting the other end of said choke to one of the two opposed stationary contact members that when said movable contact member and said one stationary contact member are in engagement, a parallel circuit is established, one branch comprising said resistor means and the other branch comprising an electrical circuit including said choke, said movable contact member and said one stationary contact member, circuit means for connecting said resistor means to the field winding and for connecting said resistor means and said field winding to a source of voltage, means for so connecting the field winding to the choke and to the other of the two opposed stationary contact members that when these two contact members are in engagement, another parallel circuit is established, one branch comprising the field winding and the other branch comprising an electrical circuit including said choke, said movable contact member and said other stationary contact member, said movable contact member having a contact portion facing said other stationary contact member and being of gold having a nickel content within the range of 3 to 10%, an operating coil responsive to the output voltage of the generator for effecting an actuation of the movable contactmember with respect to the two opposed stationary contact members and means for biasing the movable contact member against the action of the operating coil.

3,484,675 5 6. A switching arrangement as defined in claim 5, References Cited wherein said choke has an inductance between UNITED STATES PATENTS H 2,689,936 9/1954 Kirsch et a1 317-112 X 40 and 60 1 3,252,014 5/1966 Seulen 317-112 X 5 whereby I is the average value of the current through said ORIS RADER Pnmary Exammer field Winding, H. HUBERFELD, Assistant Examiner 7. A switching arrangement as defined in claim 5, US Cl XR wherein said one stationary contact member is of silver containing copper less than 4%. 10 200166; 317-11; 322-70 

